This application relates to a hydraulic drive motor for use in a high-pressure environment. In particular, the lubricant for the motor bearings references the current pressure in the high-pressure environment so that the lubricant may flow out of or into the motor and through the bearings.
Industrial chemical processes often occur in reactor vessels and require agitation to aid chemical reactions. For example, agitation may provide for homogenous mixing, or for uniform suspension of materials having different densities or phases such as emulsions or solids suspended in a liquid. In general, agitators typically include one or more propellers or impellers inside the vessel that are attached to a rotating shaft. The shaft extends out through the wall of the vessel to a motor that rotates the shaft and, in turn, rotates the impellers or propellers. One or more bearing assemblies, generally near the vessel wall, hold the shaft in place and allow it to rotate freely and steadily under various rotational, transverse, and thrust loads.
It is desirable that an agitator provide consistent performance with few failures. Major industrial processing plants are extremely complex and very expensive to operate. A breakdown at one vessel can stop the operation of a major portion of a plant, and disassembly (and reassembly) of an agitator drive for repairs often takes a long time and can destroy the batch being processed in the vessel. Even worse, a breakdown in the middle of a batch may require that the vessel be carefully and laboriously cleaned before processing may resume.
Where the conditions inside the vessel are severe, such as where the temperature and pressure inside the vessel are both very high, a conventional agitator drive system may not provide acceptable reliability. For example, the motor for a drive system is typically located in a low-pressure area, and the drive shaft passes from the motor into the vessel so that there generally must be seals, packing, and/or bearings at the point where the shaft passes through the wall of the vessel. Seals and packing are prone to quick degradation under severe conditions where they are placed in high temperatures or across high-pressure differentials. In addition, the seals, packing, or bearings must be properly lubricated, and under severe conditions, the lubricants may degrade or may even leak into the interior of the vessel, contaminating the process.
Conventional solutions may not be adequate to address such problems caused by severe conditions. For example, pusher mechanical seals are often used at the vessel wall between areas of high and low pressure. These seals generally rely, however, on elastomers, which are inappropriate materials for high-temperature applications. Metal bellows (or non-pusher) seals are often used where high temperatures are expected, but they do not generally work well under high pressures. Packing materials may also be provided around a shaft where it enters a vessel. While such a solution again works well under high pressure, it can cause problems where temperatures are elevated. For example, high clamping forces around the packing material help form a tight seal that can withstand high pressure, but the forces also create friction that produces additional heat. When combined with high temperatures in the vessel, this friction can cause rapid destruction of the materials.
Placing the drive systemxe2x80x94motor and allxe2x80x94entirely in side the vessel solves the problem of sealing across a high-pressure differential, but it is not generally acceptable. The drive motor will likely be less amenable to severe conditions than are the bearings that support the shaft because it contains bearings and other components that may not handle high temperatures or a corrosive environment well. And placing the entire drive system in the vessel simply places the bearings entirely inside the high-temperature, and potentially corrosive, conditions. In addition, access to the drive is more difficult when it is entirely inside the vessel. Moreover, the problem of potential contamination of the vessel may be worsened, particularly where the motor is hydraulically powered.
One solution to the problem is to break the shaft in two, placing the motor and part of the shaft outside the vessel, and the other part of the shaft inside the vessel, so that no portion of the drive passes through the vessel wall. The two parts of the shaft may be coupled through the vessel wall magnetically. The motor""s shaft outside the vessel may be attached to large magnets, and the drive shaft attached to the agitator inside the vessel may be attached to matching magnets. The sets of magnets may be positioned on each side of a protruding area of the vessel wall so that rotation of the motor induces rotation of the agitator by magnetic coupling.
This xe2x80x9cmagnetic couplingxe2x80x9d approach, however, is expensive and allows only limited torque to be delivered to the agitator, and still requires that the bearings supporting the shaft be located in the hostile environment of the vessel. As a result, it too may require that the bearings be made of special, expensive materials, may result in premature bearing failure, and may produce contamination of the vessel. Moreover, because the coupling force is inversely proportional to the square of the wall thickness between the magnets, there will be a practical limit to the level of coupling that can occur through a wall that is thick enough to maintain the integrity of the vessel. Furthermore, as torque requirements increase, the magnets may need to be placed further from the shafts so that the container through which the magnets operate must get larger, and its wall thickness must increase to contain the vessel pressure. As a result, practical torque and size limitations constrain the general applicability of magnetically coupled drives.
Accordingly, there is a need for an agitator drive system that can provide reliable operation to vessels that house severe conditions with little or no risk of pressure loss or of contaminating the contents of the vessel. In addition, there is a need to provide such a drive in a sealless system that can use conventional materials and parts. Furthermore, there is a need to provide a motor for such a drive that can operate reliably in a high-pressure atmosphere in which the pressure varies over time.
In general, a hydraulically operated motor is described that can be operated economically in a high-pressure atmosphere. The motor is configured so that the pressure around the motor does not prevent lubricant inside the motor from flowing through the motor bearings. In particular, lubricant is provided to the motor across an air gap so that the pressure of the lubricant is intrinsically referenced to the pressure surrounding the motor, even as that pressure varies.
In one embodiment, a hydraulically operated motor for use in a high-pressure environment is described. The motor comprises a motor housing defining an interior portion in which a first bearing is positioned, and a drive shaft rotatably mounted in the first bearing. A first fluid receptacle is in fluid communication with at least one surface of the first bearing, and a first fluid supply conduit provides fluid to the first fluid receptacle, and is spaced apart from the first fluid receptacle by an air gap in the high-pressure environment. The conduit may extend through a wall of a pressurized housing from an areas of substantially lower pressure than the high-pressure environment. In addition, a case drain in fluid communication with the first fluid receptacle may be provided in the motor housing, and the first fluid receptacle may comprise the case drain.
In yet another embodiment, a conduit may be located between the first fluid receptacle and the case drain so that fluid introduced into the first fluid receptacle may lubricate the first bearing. In addition, the first fluid receptacle may comprise an upwardly opening cup, and the first fluid supply conduit may terminate above the cup and drop fluid into the cup. The motor may also comprise a second bearing in the motor housing, a second fluid receptacle in fluid communication with at least one surface of the second bearing, and a second fluid supply conduit for providing fluid to the second fluid receptacle and spaced apart from the second fluid receptacle by an air gap in the high-pressure environment. The first and second fluid receptacles may also comprise a single common receptacle.
In another embodiment, a method for lubricating a motor having a bearing in a high-pressure environment is disclosed. The method may comprise providing a fluid receptacle in fluid communication with at least one surface of the bearing, and directing a flow of lubricating fluid into the fluid receptacle across an air gap in the high-pressure environment. The lubricating fluid may also be collected and recirculated, and may be introduced into the high-pressure environment from an area of substantially lower pressure. The lubricating fluid may also be directed into the fluid receptacle as a mist, and lubrication may cease when a predetermined amount of lubricating fluid is in the fluid receptacle.